pub fn odd_fibnacci_sum(threshold: u32) -> u32 {
    let mut a = 0; // F(0)
    let mut b = 1; // F(1)
    let mut sum = 0;

    while a < threshold {
        if a % 2 != 0 {
            sum += a; // 如果是奇数，累加
        }
        let next = a + b; // 计算下一个斐波那契数
        a = b; // 更新 F(n-1)
        b = next; // 更新 F(n)
    }

    sum
}